It is known that exhaust gases from internal combustion engines contain substances which are harmful to the environment and which can pose a threat to public health. For many years, a sustained effort has been made within the automotive industry to reduce the release to the atmosphere of harmful substances carried in exhaust gases, both by modifying the combustion process itself to give a reduced yield of harmful combustion products, and by treating the exhaust gases before their emission into the atmosphere, for example by providing a catalyst to induce chemical breakdown of the harmful constituents, particularly the oxides of nitrogen (NOx), into benign compounds.
One strategy for reducing NOx emissions, known as selective catalytic reduction or SCR, involves the introduction of a reagent comprising a reducing agent, typically a liquid ammonia source such as an aqueous urea solution, into the exhaust gas stream. The reducing agent is injected into the exhaust gas upstream of an exhaust gas catalyst, known as an SCR catalyst, typically comprising a mixture of catalyst powders such as titanium oxide, vanadium oxide and tungsten oxide immobilised on a ceramic honeycomb structure. Nitrogen oxides in the exhaust gas undergo a catalysed reduction reaction with the ammonia source on the SCR catalyst, forming gaseous nitrogen and water. An example of an SCR system is described in the Applicant's European Patent Application Publication No. EP-A-2131020, the contents of which are hereby incorporated by reference.
SCR systems typically include a reagent dosing pump assembly for delivering reagent to the exhaust gas stream. Examples of such pumps are described in the Applicant's European Patent Application Publication No. EP-A-1878920, the contents of which are hereby incorporated by reference.
In one known reagent pump assembly, a solenoid-actuated pumping arrangement is provided to increase the pressure of the reagent, and the pump includes an atomising nozzle that receives the reagent from the pumping arrangement and delivers it from an outlet end into the exhaust gas stream. The nozzle is close-coupled to the pumping arrangement, so that the nozzle and the pumping arrangement form a single unit. The outlet end of the nozzle may be positioned directly in the exhaust gas stream, so that the pumping arrangement is located close to the outside of the exhaust pipe that conveys the exhaust gases.
It will be appreciated that, in such a case, the reagent dosing pump is exposed to the high temperatures that arise in the vicinity of the exhaust system, and so the reagent can be subjected to high temperatures, in use.
The maximum temperature at which urea-based reducing agents can be used is somewhat limited. Urea crystals tend to precipitate when the temperature of the solution is greater than approximately 70° C. Precipitation is undesirable because the precipitates can cause blockages in the delivery system, for example in the small-diameter outlets typically provided in the outlet end of the atomising nozzle. In addition, the formation of precipitates alters the concentration of the remaining solution, so that the effective quantity of ammonia delivered to the exhaust flow becomes uncertain. This could lead to inefficient catalysis and an insufficient reduction in NO emissions.
It is therefore desirable, in many cases, to provide cooling means to cool the reagent in an SCR system and, in particular, in the reagent dosing pump, to prevent overheating of the reagent. Furthermore, when solenoid-actuated pumping arrangements are used, it is also desirable to cool the solenoid coil since the performance of solenoid actuators can decrease at high temperatures.
In some arrangements, the reagent dosing pump of an SCR system may be mounted on the exhaust pipe under the body of a vehicle. Some cooling of the exhaust gases occurs as the gases flow from the engine to the location of the reagent dosing pump, which limits to a degree the temperature to which the reagent dosing pump, and hence the reagent, is exposed. In such arrangements, sufficient cooling of the reagent dosing pump may be possible by virtue of the cooling air-flow around the reagent dosing pump, and/or by providing suitable insulating means to reduce heat transfer from the exhaust pipe to the regent dosing pump.
In other arrangements, it is desirable to locate the reagent dosing pump in the engine compartment of the vehicle. In these cases, the reagent dosing pump is exposed to higher temperatures, due to the closer proximity of the dosing pump to the engine, and it is more difficult to provide a cooling air flow to the reagent dosing pump. Accordingly, the risk of the reagent overheating in use is higher than in an under-body arrangement.
The latest SCR reagent dosing systems (herein referred to as a “doser”) require a coolant supply, a coolant outlet, and a reagent inlet (to the dosing system pump assembly) to be provided. Reagent in such dosing systems is transported to the doser via a pipe.
As noted above, due to high ambient temperature environments (for example within the engine bay near exhaust manifold) near and at the doser, the reagent feed pipe needs to be protected from heat to avoid boiling of the reagent. An additional and more extreme heating effect may also occur after ignition off (i.e. on engine shut down or during periods when the engine may be off such as in a Start-Stop energy efficient engine system), when coolant flow ceases and the heat soak effect from the nearby exhaust manifold and engine block means there is a large heat source. Additionally, in some environments (e.g. in northern latitudes) low ambient temperatures may be experienced requiring that the reagent pipe be protected from the cold and ideally provided with heat energy in the event that the reagent is frozen.
In known systems, connection of the two inlets (coolant fluid inlet and reagent fluid inlet) and one outlet (coolant fluid outlet) to the pump assembly have been by relatively large individual connectors. This represents a relatively bulky solution which may be incompatible with the production environment which can be tight and compact and subject to space constraints. Given such a lack of space, it can be difficult to screw individual connectors to the doser in a production embodiment (e.g. during manufacture or during in-service maintenance). Connectors can also be pressed or fitted by other suitable means.
It is therefore an object of the present invention to provide a connector element for connecting a pump assembly for use in a selective catalytic reduction system to a reagent supply of reagent fluid that overcomes or substantially mitigates the above mentioned problems.